The present invention relates to a photosensitive composition. More particularly, the present invention relates to a photosensitive composition containing an o-naphthoquinonediazide compound, which is suitable for the production of lithographic printing plate, letterpress printing plate, IC, photomask, etc., which is capable of producing a visible image immediately after exposure, and which is excellent in sensitivity, image visibility after exposure, ball-point pen resistance, and chemical resistance.
Light-sensitive compositions containing an ester compound of o-naphthoquinonediazide sulfonate and a novolak resin as a photosensitive composition have been widely used for industrial production of lithographic printing plates and photoresists. These photosensitive compositions containing o-naphthoquinonediazide compound, however, have the following defects.
After the exposing operation under a yellow safety lamp, photosensitive o-naphthoquinonediazides having a yellow color become a colorless or pale yellow photodissociated component in which the yellow color is faded, but it is difficult to distinguish the exposed area from the unexposed area. For this reason, it is difficult or impossible for a platemaker to know whether or not a plate has been exposed when the work is suspended in the process of exposing a multiplicity of plates at the same time. Similarly, when a large plate is exposed many times in what is called a photocomposing method, for example, for making a lithographic printing plate, the platemaker cannot confirm what part has been exposed. For this reason, an operational miss is often caused, thereby greatly lowering the working efficiency.
The following arts of forming a visible image immediately after exposure by using a photosensitive composition, in other words, the arts for improving the above-described defects and imparting the image visibility after exposure to a photosensitive composition by using various materials, are known.
For example, U.S. Pat. Nos. 2,066,913 disclose a composition of using various reducible salts in the form of a mixture with a diazo compound; Japanese Patent Publication (KOKOKU) No. 2203/1965 discloses a photosensitive sheet for forming a visible image after exposure by using a photosensitive diazo compound and a basic indicator; Japanese Patent Publication (KOKOKU) No. 3041/1974 discloses a photosensitive composition comprising a positive-working diazo resin and a merocyanine dye; Japanese Patent Publication (KOKOKU) No. 21093/1965 discloses a printing original plate which is imparted with photosensitivity in advance by o-naphthoquinonediazide and which contains in the photosensitive layer an organic coloring agent for changing the tone when the pH is 2.5 to 6.5: Japanese Patent Publication (KOKOKU) No. 36209/1975 discloses a photosensitive copying layer containing o-naphthoquinonediazide sulfonate or o-naphthoquinonediazide sulfamide in which o-naphthoquinonediazide-4-halogenide sulfonate is 10 to 75 wt % and an organic compound having a salt formability as a dye is 1 to 50 wt % both based on the total content of the o-naphthoquinonediazide compound; and Japanese Patent Application Laid-Open (KOKAI) No. 62444/1980 discloses a photosensitive composition which contains an ester compound of phenol substituted by an electron absorbing substituent and o-naphthoquinonediazide-4-sulfonate, and an organic dye for changing the color tone by the interaction with a photodecomposition product of the o-naphthoquinonediazide-4-sulfonate compound.
The image visibility after exposure of the photosensitive compositions mentioned above, however, is still insufficient. In addition, the image visibility after exposure is lowered with passage of time too much for practical use.
The photosensitive compositions containing a halomethyloxadiazol compound as described in Japanese Patent Laid-Open Nos. 74728/1979 and 77742/1980 and a photosensitive composition containing a halomethyl-s-triazine compound and a color-changing agent which changes the color tone by the interaction with the photodecomposition product of the compound as described in Japanese Patent Application Laid-Open (KOKAI) Nos. 36281/1973 and 32070/1980 have recently become widespread because they can form a distinct visible image immediately after exposure and they are excellent in the stability with passage of time. In Japanese Patent Application Laid-Open (KOKAI) NO. 88942/1985, a combination of 2-trichloromethyl-5-(p-methoxystyryl)-1,3,4-oxadiazol and an organic acid, and a combination of 2,4-bis-(trichloromethyl)-6-p-methoxystyryl-s-triazine and an organic acid as components of photosensitive compositions are disclosed.
These photosensitive compositions, however, are also insufficient in the image visibility after exposure, especially, when the exposure is small. On the other hand, if the amount of visible image forming agent added is increased in order to enhance the image visibility after exposure, the sensitivity is unfavorably lowered.
A photosensitive composition is also required to have resistance to various chemicals used at the time of printing, for example, a counter-etching agent and a plate cleaner (the resistance will be referred to as "chemical resistance" hereinunder), and it is known that the chemical resistance of a photosensitive composition is improved by adding a vinyl polymer having a phenol hydroxyl group or a derivative thereof to the photosensitive composition.
Addition of a vinyl polymer having a phenol hydroxyl group, however, inconveniently lowers the image visibility after exposure and the sensitivity.
Another conventional problem is as follows. At the time of photocomposing, due to register of the film-manuscript, the position of the manuscript is marked on the photosensitive layer with a ball-point pen using oily ink. At this time, the solvent of the ink of the ball-point pen seems to erode the photosensitive layer, and after development, the mark appears at the image area and further on the printed sheet.
A photosensitive composition having a photosensitive layer which is hard to erode by the ink solvent of a ball-point pen (hereinunder referred to as "ball-point pen resistance") is, therefore, strongly demanded.
As described above, various means for satisfying the demands on a photosensitive composition have been proposed. However, if one requirement is met, another cannot be satisfied. It is thus difficult to keep a plurality of required properties with good balance.
As a result of various studies undertaken by the present inventors so as to solve the above-described technical problems and to provide a photosensitive composition which satisfies all the properties required such as sensitivity, image visibility after exposure, chemical resistance and ball-point pen resistance without sacrificing any of the properties, it has been found that a photosensitive composition containing a quinonediazide compound, an s-triazine compound having a specific skeleton, a dye for changing the tone by the interaction with a photodecomposition product, and two resins, namely, a novolak resin having a specific composition and a vinyl polymer having a specific skeleton is excellent in image visibility after exposure, especially when the exposure is small sensitivity, chemical resistance and ball-point pen resistance. On the basis of this finding, the present invention has been achieved.